1. Field of the Invention
The invention relates to an optical circulator, and more particularly to an optical circulator with three ports for use in optical communication.
2. Description of the Related Art
In a three port optical circulator, an optical signal input at the first port will be transmitted to the second port. An optical signal input at the second port will be transmitted to the third port.
With reference to FIG. 1, a compact circulator is disclosed in U.S. Pat. No. 5,204,771 by Koga. This circulator shows an improvement over the previous one since the two optical paths can be in close proximity, and the first and third ports 27, 28 are parallel.
Unfortunately, this device still suffers from a disadvantage. If the first and third ports 27, 28 are very close together, the first and third fibers will have to share a common lens for collimating and focusing. It is impossible for a single lens to perform adequately for both fibers. The difficulty can be traced to the fact that the light beams coupled to the first and third ports are parallel, and a single lens cannot focus two parallel beams to two different points. Therefore, the circulator has a problem of coupling angle.
The invention provides a compact optical circulator with three ports, wherein a propagation director is provided to solve the problem of coupling angle. The propagation director can focus two parallel beams appearing on the same side of the compact optical circulator to two different points (i.e. to two different fibers).
It is an object of the present invention to provide a compact optical circulator, including a dual-core collimator, a propagation director, a first birefringent device, a first polarization rotator, a second birefringent device, a second polarization rotator, a third birefringent device and a single-core collimator.
The invention further provides a compact optical circulator with three ports, wherein a reflective compensator is provided to eliminate the polarization mode dispersion (xe2x80x9cPMDxe2x80x9d).
It is another object of the present invention to provide a compact optical circulator, including a dual-core collimator, a propagation director, a first birefringent device, a first polarization rotator, a second birefringent device, a second polarization rotator, a compensator, a third birefringent device and a single-core collimator.
A feature of the invention is that one beam from the first port to the second port is normally incident on the first birefringent by passing through the propagation director. Thus, the compact optical circulator of the invention has an advantage of reduction of polarization dependent loss.
Another feature of the invention is that the first and second polarization rotators are the non-reciprocal rotators respectively.
The compact optical circulator of the invention has another advantage of reduction of production cost. A non-reciprocal rotator aligning with the optical axis of the birefringent device replaces the use of a reciprocal rotator and a non-reciprocal rotator, and thus the invention reduces production costs.
The compact optical circulator of the invention has another advantage of elimination of the polarization mode dispersion utilizing a reflective compensator.